Fast and slow speed driving means for electric lifts



Aprll 5, 1949. W, Gl FQULDS 2,466,167

FAST AND SLOW SPEED DRIVING MEANS FOR ELECTRIC LIFTS Filed March 21,1946 Patented Apr. 5, 1949 FAST AND SLOW SPEED DRIVING MEANS FORELECTRIC LIFTS William Geoffrey Foulds, Colne, England Application March21, 1946, Serial No. 655,991 In Great Britain February 6, 1945 Section1, Public Law 690, August 8, 1946 Patent expires February 6, 1965 (Cl.S18-8) 4 Claims. l

This invention relates to fast and slow speed driving means for electriclifts and the like such as electric cranes where a relatively wide rangeof fast and slow speeds is required and A. C. supplyis available.

Hitherto, such speed variation has been obtained either by variablespeed gearing or by the use'of variable speed electric motors, usuallyD. C. motors owing to the known limitations of speed variation of A. C.motors. The use of changes-peed gearing has many inherent disadvantagesalso'the use of D. C. variable speed motors entails the additionalinstallation of a rotary converter or a very large rectifier.

The objectof the present invention is an improved driving means havingthe advantages of a wide range between fast and slow speedswithout thedisadvantages of gearing or D. C. converter as above explained.

Accordingto the invention fast and slow change-speed driving means forelectric lifts and like mechanism operating on A. C. supply coinprisesin combination alternative fast A. C. and slow D. C. driving motors, alow wattage means for producing high and low voltage D. C. supply fromthe A. C. supply, a regenerative braking circuit for the D. C. motorhaving its resistance element permanently shunted across the armature, arectiiier shunt protector circuit for the eld of the D. C. motor, andswitch means for selectively `operating one or other of the motors andfor changing from fast A. C. drive to slow D. C. drive including acontrolling relay in and actuated by the said regenerative brakingcircuit and arranged to break and make the high voltage D. C. fieldsupply to the D. C. motor until the regenerative voltage reaches thatfor the predetermined slow speed and thereafter to complete and maintainthe high voltage D. C. supply to the field and a low voltage D. C.supply to the armature.

In the drawings iiled herewith:

Fig. l is a wiring diagram illustrating one eX- ample of the invention;and

Fig. 2 is a fragmentary View showing a modication.

.As shown in the drawing I represents a 3- phase 400 volt A. C. mainssupply with the usual ultimate limit switch Ii, contactors I 2 andreversing switch I3 for the A. C. motor I4. The controlling mechanism iselectrically operated by transformer I5 and rectifier l5 which provides220 volt D. C. supply. A slow speed D. C. motor I'I with armature Ila,shunt field IIb and series field IIc is provided, coupled to the shaftof the A. C. motor or built into one unit and this has 2 a reversingswitch E3 coupled for simultaneous action to the reversing switch 3 ofthe A. C. motor. A low voltage and low wattage D. C. supply is providedby a tra? former iii and a metal rectifier rEhe armature ila of the D.C. motor is permanently shunted by vibrating type (make-and-break) relay2i and a braking resistance forming part of the regenerative circuit,the relay 2i including a switch in the circuit of the iield l''b of theD. C. motor and controlling high voltage D. C. supply to such eld fromthe rectifier Tn the circuit to the field iii; is a relay it with coil230i arranged to operate the main D. C. supply to the armature lla whichis tapped into the energising coil of the relay 2i and reaches thearmature through the reversing switch i6 aforesaid. The remainder of thediagram shows the usual arrangement of floor and cage contacts, andselecting mechanism necessary for the complete wiring installation. Adischarge rectier it is provided across the shunt field winding lll).

En operation, assuming the lift is moving under the control oi the A. C.motor, when the lift approaches the selected floor, the selectormechanisni cuts orf ythe A. C. motor and the levelling switch takescharge switching on the high voltage D. C. supply to the field lib ofthe D. C. motor approaches the selected floor, the selector mechso thatthe latter operates as a brake through the regenerative circuitincluding the resistance 22. As the instantaneous regenerative voltagewill be high, compared with the nal low D, C. running voltage for therectifier 20, the relay 2l will break the D. C. iield supply so that theflux will decay gradually through the rectier 24. The relay 2l willmake-and-break until the regenerative voltage, which is proportional tothe motor speed, falls to predetermined value, when the relay 2l finallyholds the D. C. shunt eld circuit closed. During this make-and-breakaction of the relay 2l the relay 23 will not operate as the iieldcurrent through its coil 23a never attains full value but as soon as therelay 2| has closed inally then relay 23 switches on the low voltage D.C. supply to the armature and the D. C. motor then continues to drivethe lift at the slow speed for which it is designed. The levellingswitch will stop the lift at the selected door by breaking the circuitat the reversing switch iii. Of course, if the lift has overshot thefloor, the reversing switch will reverse the operation of the D. C.motor so that after it has acted as a regenerative brake to stop thelift it will be switched on to bring the lift back to the landing on theslow speed.

In a modication, 'instead of a vibrating type make-and-break relay 2i anordinary relay is .used and a resistance 25 of relatively low value isshunted across the contacts of such ordinary relay `and the coil 23a.When the regenerative current in the coil of :the relay 2| has fallenbelow a predetermined maximum the relay 2| closes, energisingr the coil23a and closing the circuit between the armature ll'a and the rectifier.Thus the relays 2| and 23 have the sole function of determining theclosing of the armature circuit when the motor is slowed down to a safespeed for this to be done. The modification provides better brakingtorque as the eld circuit lll) is thus energised almost at its fullstrength through the shunting resistance even when the contacts of `therelay 2 l are open.

What I claim is:

l. Fast and slow change-speed driving mechanism for electric lifts andlike mechanism comprising in combination an A. C. electric motor forfast speed movement of the lift, a D. C. electric motor with aregenerative braking circuit for braking and levelling of the lift andswitch means for alternative operation of the A. C. and. D. C. motors for movement of the lift.

2. Fast and slow change-speed driving mech anism for electric lifts andlike mechanism com-- prising in combination an A. C. electric motor forfast speed movement of the lift, a D. C. electric motor with aregenerative braking circuit for braking and levelling of the lift andswitch means for yalternative operation of the A. C. and D. C.

braking and levelling of :the lift and switch means for alternativeoperation of the A. C. 'and D. C. motors for movement of the lift, saidmechanism including a rectifier connected to the A. C. supply forsupplying D. C. for the D. C. motor Iand shunted across the saidregenerative circuit, a relay operable by the said regenerative circuitand controlling the rectier circuit so that the latter can only beconnected to the D. C. motor when the regenerative voltage is below apredetermined maximum.

4. Fast and slow change-speed `driving means for electric lifts and likemechanism operating on A. C. supply comprising in combinationalternative fast A. C. and slow D. C. driving motors, a low wattagemeans for producing high and low voltage D. C. supply from the A. C.supply, a regenerative braking circuit for the D. C. motor having itsresistance element permanently shunted across the armature, a rectifiershunt :protector circuit for the iield of the D. C. motor, and switchmeans for selectively -operating one or other of the motors and forchanging from fast A. C. drive to slow D. C. drive including a.controlling vibrating type relay in and vactuated by the saidregenerative braking circuit and arranged to break and make the highvoltage D. C. eld supply to the D. C. motor until the regenerativevoltage reaches `that for the predetermined slow speed and `thereafterto complete and maintain the high voltage D. C. supply to the iield anda low voltage D. C. supply to the armature.

WILLIAM GEOFFREY FOULDS.

REFERENCES CITED The following references are of record in the file orthis patent:

UNITED STATES PATENTS

